Microwave treatment of dairy manure for resource recovery: Reaction kinetics and energy analysis.

A newly designed continuous-flow 915 MHz microwave wastewater treatment system was used to demonstrate the effectiveness of the microwave enhanced advanced oxidation process (MW/H2O2-AOP) for treating dairy manure. After the treatment, about 84% of total phosphorus and 45% of total chemical oxygen demand were solubilized with the highest H2O2 dosage (0.4% H2O2 per %TS). The reaction kinetics of soluble chemical oxygen demand revealed activation energy to be in the range of 5-22 kJ mole-1. The energy required by the processes was approximately 0.16 kWh per liter of dairy manure heated. A higher H2O2 dosage used in the system had a better process performance in terms of solids solubilization, reaction kinetics, and energy consumption. Cost-benefit analysis for a farm-scale MW/H2O2-AOP treatment system was also presented. The results obtained from this study would provide the basic knowledge for designing an effective farm-scale dairy manure treatment system.

Microwave oxidation treatment of sewage sludge.

Microwave-oxidation treatment of sewage sludge using various oxidants was studied. Two treatment schemes with a combination of hydrogen peroxide and ozone were examined: hydrogen peroxide and ozone were introduced into the sludge simultaneously, followed by microwave heating. The other involved the ozonation first, and then the resulting solution was subjected to microwave and hydrogen peroxide treatment. The set with ozonation followed by hydrogen peroxide plus microwave heating yielded higher soluble materials than those of the set with hydrogen peroxide plus ozone first and then microwave treatment. No settling was observed for all treatments in the batch operation, except ozone/microwave plus hydrogen peroxide set at 120°C. The pilot-scale continuous-flow 915 MHz microwave study has demonstrated that microwave-oxidation process is feasible for real-time industrial application. It would help in providing key data for the design of a full-scale system for treating sewage sludge and the formulation of operational protocols.

Recovery of phosphorus from dairy manure: a pilot-scale study.

Phosphorus was recovered from dairy manure via a microwave-enhanced advanced oxidation process (MW/H2O2-AOP) followed by struvite crystallization in a pilot-scale continuous flow operation. Soluble phosphorus in dairy manure increased by over 50% after the MW/H2O2-AOP, and the settleability of suspended solids was greatly improved. More than 50% of clear supernatant was obtained after microwave treatment, and the maximum volume of supernatant was obtained at a hydrogen peroxide dosage of 0.3% and pH 3.5. By adding oxalic acid into the supernatant, about 90% of calcium was removed, while more than 90% of magnesium was retained. As a result, the resulting solution was well suited for struvite crystallization. Nearly 95% of phosphorus in the treated supernatant was removed and recovered as struvite.

Effects of acidifying reagents on microwave treatment of dairy manure.

Dairy manure, acidified using organic acids (acetic, oxalic, and citric acid) were treated with microwave enhanced advanced oxidation process (MW/H2O2-AOP). The effect of a mixture of oxalic acid and commonly used mineral acids (sulfuric and hydrochloric acid) on MW/H2O2-AOP was also examined. Substantial amounts of phosphorus were released under MW/H2O2-AOP, regardless of organic acid or mineral acid used. All three organic acids were good acidifying reagents; however, only oxalic acid could remove free calcium ion in the solution, and improve settleability of dairy manure. The MW/H2O2-AOP and calcium removal process could be combined into a single-stage process, which could release phosphate, solubilize solids and remove calcium from dairy manure at the same time. A mixture of oxalic acid and mineral acid produced the maximum volume of clear supernatant and had an ideal molar ratio of calcium to magnesium for effective struvite (magnesium ammonium phosphate) crystallization process. A single-stage MW/H2O2-AOP would simplify the process and reduce mineral acid consumption compared to a two-stage operation. The results of a pilot scale study demonstrate that MW/H2O2-AOP is effective in treating manure and recovering resource from dairy farms.

Microwave enhanced advanced oxidation process for treating dairy manure at low pH.

This study investigated the treatment of dairy manure using the microwave enhanced advanced oxidation process (MW-AOP) at pH 2. An experimental design was developed based on a statistical program using response surface methodology to explore the effects of temperature, hydrogen peroxide dosage and heating time on sugar production, nutrient release and solids destruction. Temperature, hydrogen peroxide dosage and acid concentration were key factors affecting reducing sugar production. The highest reducing sugar yield of 7.4% was obtained at 160°C, 0 mL, 15 min heating time, and no H(2)O(2) addition. Temperature was a dominant factor for an increase of soluble chemical oxygen demand (SCOD) in the treated dairy manure. The important factors for volatile fatty acids (VFA) production were microwave temperature and hydrogen peroxide dosage. Temperature was the most important parameter, and heating time, to a lesser extent affecting orthophosphate release. Heating time, hydrogen peroxide dosage and temperature were significant factors for ammonia release. There was a maximum of 96% and 196% increase in orthophosphate and ammonia concentration, respectively at 160°C, 0.5 mL H(2)O(2) and 15 min heating time. The MW-AOP is an effective method in dairy manure treatment for sugar production, nutrient solubilisation, and solids disintegration.

The effects of irradiation intensity on the microwave-enhanced advanced oxidation process.

The microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was adopted in successfully treating a multitude of organic slurries. The factor of ramp rate was incorporated in this study to investigate its correlations with different nutrients release into solution from waste activated sludge. Besides the ramp rate, the amount of time the samples were held at the treatment temperature to a total of 10 minutes aided in the isolation of held temperature from ramp rates, since different ramp rates will yield different reaction times. It was found that with the exception of orthophosphate and chemical oxygen demand release, ammonia and volatile fatty acids depended highly on the ramp rates. All constituents, chemical oxygen demand, orthophosphate, ammonia and volatile fatty acids, solubilized better with longer reaction times coupled with the highest ramp rate. Besides treatment time and ramp rates, treatment temperature and hydrogen peroxide dosage also play important roles in the release of various nutrients into solution by the MW/H(2)O(2)-AOP. The results from this study can aid in design parameters for the scaling up of a continuous microwave system for the MW/H(2)O(2)-AOP.

Nutrient release from extracted activated sludge cells using the microwave enhanced advanced oxidation process.

This study investigates the effectiveness of the microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) for nutrient release and cell destruction of the extracted activated sludge cells that are EPS-free. The concentrations of ammonia and soluble chemical oxygen demand increased with an increase of microwave temperature and hydrogen peroxide dosage. Orthophosphate could be released from these extracted cells at lower microwave temperatures and lower H(2)O(2) dosages compared to our previous studies using activated sludge. Higher concentrations of carbohydrate were released into the solution with an increase of microwave temperature. For the same microwave temperatures, carbohydrate release was first increased with the addition of H(2)O(2), and then decreased as the H(2)O(2) dosages increased further. The amount of DNA in solution was a good indicator of the extent of cell damage; the high concentration of DNA released into solution after treatment indicated significant cell damage.

Treatment of dairy manure using the microwave enhanced advanced oxidation process under a continuous mode operation.

The microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was used to treat dairy manure for solubilization of nutrients and organic matters. This study investigated the effectiveness of the MW/H(2)O(2)-AOP under a continuous mode of operation, and compared the results to those of batch operations. The main factors affecting solubilization by the MW/H(2)O(2)-AOP were heating temperature and hydrogen peroxide dosage. Soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFA) increased with an increase of microwave (MW) heating temperature; very high concentrations were obtained at 90°C. Insignificant amounts of ammonia and reducing sugars were released in all runs. An acidic pH condition was required for phosphorus solubilisation from dairy manure. The best yield was obtained at 90°C with an acid dosage of 1.0 %; about 92 % of total phosphorus and 90 % of total chemical oxygen demand were in the soluble forms. The MW/H(2)O(2)-AOP operated in a continuous operation mode showed pronounced synergistic effects between hydrogen peroxide and microwave irradiation when compared to a batch system under similar operating conditions, resulting in much better yields.

Treating solid dairy manure using microwave-enhanced advanced oxidation process.

The microwave enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was used to treat separated solid dairy manure for nutrient release and solids reduction. The MW/H(2)O(2)-AOP was conducted at a microwave temperature of 120 degrees C for 10 minutes, and at three pH conditions of 3.5, 7.3 and 12. The hydrogen peroxide dosage at approximately 2 mL per 1% TS for a 30 mL sample was used in this study, reflecting a range of 0.53-0.75 g H(2)O(2)/g dry sludge. The results indicated that substantial quantities of nutrients could be released into the solution at pH of 3.5. However, at neutral and basic conditions only volatile fatty acids and soluble chemical oxygen demand could be released. The analyses on orthophosphate, soluble chemical oxygen demands and volatile fatty acids were re-examined for dairy manure. It was found that the orthophosphate concentration for untreated samples at a higher % total solids (TS) was suppressed and lesser than actual. To overcome this difficulty, the initial orthophosphate concentration had to be measured at 0.5% TS.

Nutrient release from fish silage using microwave-enhanced advanced oxidation process.

The microwave-enhanced advanced oxidation process was used to treat fish silage for nutrient release and solids reduction prior to its use as a fertilizer for greenhouse operations. Fifteen sets of experiments with varying hydrogen peroxide dosages and treatment temperatures were conducted to evaluate the effectiveness of the process on the solubilization of fertilizer constituents. It was found that up to 26% of total Kjeldahl nitrogen could be released as ammonia with 6% hydrogen peroxide dosage at 170 degrees C. An increase of nitrate/nitrite concentration was observed with higher hydrogen peroxide dosage and higher microwave temperature; the highest concentration of 10.2 mg L(- 1) nitrates/nitrites was achieved at at 170 degrees C and 6% H(2)O(2) dosage. Up to 20 +/- 9.5% of total chemical oxygen demand was reduced at temperatures between 120 and 170 degrees C. Large quantities of volatile fatty acids were generated at lower temperatures, corresponding to an increase in soluble chemical oxygen demand, but not at higher temperatures. The treatment of fish silage using the microwave-enhanced advanced oxidation process appears to be promising.

Real-time treatment of dairy manure: implications of oxidation reduction potential regimes to nutrient management strategies.

A pilot-scale sequencing batch reactor (SBR) was operated at a dairy farm to test real-time based control in winter operation conditions. A combination of high loading and low oxidation reduction potential (ORP) conditions in the aerobic stage of SBR treatment (an end value of -50 to -150 mV) inhibited nitrification while maintaining carbon removal. After a period of over-aeration over several cycles, the ORP at the end of the aerobic stage increased to values of 50-75 mV. Subsequently, nitrification was observed, accompanied by higher total cycle times. Significant increase in removal efficiencies of ammonical nitrogen (alpha<0.0001) and chemical oxygen demand (alpha<0.001) were observed for the high ORP phase. It is postulated that higher ORP regimes are needed for nitrification. In low ORP regimes, nitrification is absent or occurs at an extremely low rate. It is also noted that nitrifying systems treating high strength animal manure can possibly lead to unacceptably high levels of effluent nitrate+nitrite nitrogen (NO(x)-N). Two manure management schemes are proposed that give the farmer an option to either retain the nutrients, or remove them from the wastewater. Some advantages and disadvantages of the schemes are also discussed.

Treatment of sewage sludge in a continuous-flow radiofrequency-oxidation system.

This study explored the applicability of a pilot-scale continuous-flow radiofrequency (RF) heating system to treat sewage sludge by the RF-oxidation process (RF/H2O2). Depending on temperature and hydrogen peroxide dosage, high amounts of soluble chemical oxygen demand and volatile fatty acid were produced, and phosphates, nitrogen, and metals were solubilized. A high temperature and/or a higher H2O2 dosage implemented in this system yielded high solubilization of organic matters. Orthophosphate increased with an increase in treatment temperature up to 60°C, its concentration decreased as temperature further increased. There was little effect on orthophosphate release by varying H2O2 dosage. The efficiency of the RF/H2O2 process was comparable to the microwave (MW) enhanced advanced oxidation process (MW/H2O2-AOP), in terms of solids disintegration and nutrient release; however, the solubilization rate was lower for RF/H2O2 process. The overall energy consumed by the RF/H2O2 process was higher than the MW/H2O2-AOP.

Radiofrequency-oxidation treatment of sewage sludge.

A novel thermal-chemical treatment technology using radiofrequency heating and oxidants (hydrogen peroxide, ozone and a combination of both) was used for the treatment of sewage sludge. This was to evaluate the process effectiveness on cell disintegration and nutrient release of sludge, physical property changes such as particle size distribution, dewaterability and settleability, and their inter-relationships. The effectiveness of treatment processes was in the following order, from the most to least: thermal-oxidation process, oxidation process and thermal process. The thermal-oxidation process greatly increased cell disintegration and nutrient release, improved settleability, and decreased particle sizes. The treatment scheme involving ozone addition followed by hydrogen peroxide and radiofrequency heating yielded the highest soluble chemical oxygen demand, volatile fatty acids, ammonia and metals, while proffering the shortest capillary suction time and excellent settling properties.

Solubilization of municipal anaerobic sludge using microwave-enhanced advanced oxidation process.

The effect of microwave enhanced advanced oxidation process on the release of nutrients and solids disintegration from municipal anaerobic sludge was investigated. Three levels of temperature (160, 120, and 80 degrees C) and two sets of pH, (7.8 and 4) were selected and tested at a microwave heating time of 5 minutes and hydrogen peroxide dosage of approximately 1 mL per 1% total solids. Total chemical oxygen demand concentrations in samples decreased after the treatments at pH 4, while they remained the same as the initial at pH 7.8. The soluble chemical oxygen demand concentrations increased in all sets, regardless of treatment conditions. There was an increase in orthophosphate concentration with an increase of temperature at pH 4, while a decrease of orthophosphate at pH 7.8 was observed. Ammonia concentration also increased with an increase of temperature at pH 4. A small amount of ammonia was converted to nitrates/nitrites in the absence of acid. Acid addition helped in the destruction of sludge solids. Low pH and high temperature gave the highest nutrient release and solids destruction.

Factors affecting microwave-enhanced advanced oxidation process for sewage sludge treatment.

The microwave-enhanced advanced oxidation process (MW/H(2)O(2)-AOP) was applied to sewage sludge for nutrient solubilization and solids' disintegration. Four factors, temperature, hydrogen peroxide dosage, mixing, and solids concentration were chosen for a screening experiment, and were ranked according to their significance of influence on the process. In general, temperature and hydrogen peroxide dosage are the two significant factors affecting the process, while mixing is the least significant factor. Temperature was the most significant factor for the release of orthophosphate, and hydrogen peroxide dosage was most important in ammonia release. Solids disintegration, in terms of soluble chemical oxygen demand (SCOD), was largely dependent on temperature and hydrogen peroxide dosage. For volatile fatty acids (VFA) release, mixing was the most significant factor. At higher temperatures with mixing, more VFA was released into the headspace, resulting in less VFA retained in the solution. The best results of solids' disintegration and nutrient release were obtained at 120 degrees C, and 0.80 g H(2)O(2)/g dry sludge.

Role of mixing on microwave-enhanced advanced oxidation process in treating sewage sludge.

The microwave enhanced advanced oxidation process (MW/H2O2-AOP) was used for the release of nutrients and the disintegration of suspended solids from both anaerobic sludge and aerobic sludge. The purpose of this study was to determine the effects of mixing on the performance of the process, in terms of soluble ammonia, orthophosphate and soluble chemical oxygen demands. Experiments were conducted on sludge samples with various total solids concentrations (1.1-3.7%) and hydrogen peroxide dosage (1% per 1% of total solids) at 80 degrees C of microwave temperature and five minutes of heating time. The results indicated that mixing affected solids disintegration and nutrient solubilization of sewage sludge, regardless of the sludge used, anaerobic or aerobic. However, the effects of mixing on the MW/H2O2-AOP were dependent on the total solids concentration of the sludge. A paired t-test was performed on data for aerobic sludge: at 2.9% of total solids (TS), the difference for solubilization of nutrients and solids disintegration was statistically significant at a 95% confidence level between mixing and non-mixing samples. At a lower TS of 1.7% only soluble chemical oxygen demand showed significant difference between mixing and non-mixing. The results suggest that, for sludge with higher solids content, the MW/H2O2-AOP can be more effective if a mixing device is implemented.

Sewage sludge treatment using microwave-enhanced advanced oxidation process.

A microwave-enhanced advanced oxidation process using hydrogen peroxide (MW/H(2)O(2)-AOP) was used for the release of nutrients and the destruction of solids from secondary municipal sewage sludge in this study. Using a computer statistical software package for designing experiments and for data analyses, four factors including microwave heating temperature, heating time, hydrogen peroxide dosage, and sludge solids content were examined. Experiments were performed at sludge solids content of 0.5, 1.5 and 2.5%, heating temperature of 80, 100 and 120 degrees C, heating time of 1.5, 3 and 9 minutes, and hydrogen peroxide dosage of 0, 1 and 2 wt %, respectively. Overall, the maximum solubilization of nutrients was obtained at 2.5% of total solids content, 2 wt % of hydrogen peroxide, 5 min. of microwave heating and at 120 degrees C. The most significant factor for the solubilization of nutrients using the microwave enhanced advanced oxidation process was the initial sludge concentration. Hydrogen peroxide dosage was also a very significant factor. The maximum yield occurred at an extended heating period of five minutes in this study. Nevertheless, the results indicated that the nutrient release and disintegration of solids were also very substantial over heating periods of 1.5 and 3 minutes. Even with a heating period of 1.5 minutes, the yield was estimated to be about 70% that of the 5 minute heating.

Factors affecting nutrient solubilization from sewage sludge using microwave-enhanced advanced oxidation process.

A microwave-enhanced advanced oxidation process using hydrogen peroxide (MW-H2O2-AOP) was used for the solubilization of phosphate and ammonia from secondary municipal sludge. Two sets of experiments were performed to determine the factors affecting nutrient solubilization from sewage sludge. Four factors--microwave heating temperature, heating time, hydrogen peroxide treatment, and sulphuric acid treatment--were incorporated into a screening design to determine which factors were significant for maximizing nutrient solubilization. For phosphorus, the three most significant factors, following the order of significance, were (i) microwave heating temperature, (ii) the combined effect of microwave heating temperature and hydrogen peroxide hydrogen peroxide addition, (iii) microwave heating temperature, and (iv) sulphuric acid addition.

Solubilization of blood meal to be used as a liquid fertilizer.

The solubilization of blood meal by means of the microwave-hydrogen peroxide enhanced advanced-oxidation process (MW/H(2)O(2)-AOP) was studied. It was found that over the treatment temperature range of 60 to 120 degrees C, solids particle reduction, ammonia and orthophosphate production could be achieved by this process. Large protein molecules were broken down into intermediate compounds with low molecule weights, ammonia and nitrate. Intermediate compounds, such as peptides and amino acids, can also be easily converted to nitrogenous nutrients for plant growth by bacteria. Soluble nitrogen content increased with an increase in microwave heating temperature when acid was added; significant amounts of ammonia were obtained at higher temperatures. Nitrate decreased in concentration with an increase of treatment temperature. Orthophosphate concentrations increased after the advanced-oxidation process (AOP) treatments, with and without acid addition; but were more pronounced with acid addition. Maximum solubility of chemical oxygen demand (COD) occurred at 80 degrees C. Without the addition of acid, soluble COD decreased due to protein denaturation and coagulation out of the solution.

Sewage sludge nutrient solubilization using a single-stage microwave treatment.

The effects of an advanced oxidation process combining microwave, hydrogen peroxide and acid hydrolysis in a single stage (MW/H2O2/H+ -AOP) on the process efficiency of sewage sludge treatment and nutrient recovery were investigated. At lower temperature regimes (60-80 degrees C), the soluble phosphate was substantially higher in a two-stage process than in a single stage MW/H2O2/H+ -AOP process. However, higher soluble phosphate concentration was obtained for single-stage treatment at the higher operating temperature regimes (100-120 degrees C). With the addition of an inorganic acid, a very high yield of soluble phosphate was obtained in the solution at 120 degrees C. In tests with acid addition, soluble ammonia increased as temperature increased. For single stage MW/H2O2/H+ -AOP, maximum soluble ammonia was obtained at 120 degrees C. Significant concentrations of soluble COD were also obtained in this treatment. A threshold temperature of 80 degrees C was observed, at which all of the COD could be solubilized. However, at higher temperatures (100-120 degrees C), further oxidation processes occurred to form carbon dioxide, resulting in decreased amounts of soluble COD in the solution.